1. Field of the Invention
This invention relates generally to catalytic combustors for use with gas turbines. More specifically, the invention provides a heat exchange system for rapidly bringing the temperature of a combustor to a level where efficient catalytic reactions may occur.
2. Discussion of the Related Art
Catalytic combustion makes possible extremely low emissions of pollutants from gas-powered turbine generators, particularly of oxides of nitrogen (NOx). Properly designed catalytic combustors can deliver both low NOx and low carbon monoxide (CO) emissions, in contrast to conventional combustors which may suffer from high NOx and/or high CO.
Gas turbine systems have been previously proposed in which an air/fuel mixture is compressed by a compressor, and then reacted in a catalytic combustor. For example, U.S. Pat. No. 4,754,607 describes a self-contained energy center or cogeneration system which converts chemical energy into mechanical, electrical, and heat energy. The fuel, preferably a gaseous fuel such as natural gas, is mixed with air in a mixer, and then the resulting mixture enters the compressor. The compressor compresses the air/fuel mixture and outputs the compressed mixture to the cold side of a heat exchanger in which the mixture becomes heated. The heated, high-pressure mixture is then delivered to the combustion chamber of a catalytic combustor. The resulting products of combustion are directed to the inlet of an expansion turbine mounted on the compressor shaft. After powering the turbine, the hot combustion gases are directed through the hot side of the heat exchanger, whereupon those gases supply the heat which is transferred to the cooler air/fuel mixture passing through the cold side of the heat exchanger. In this case, the turbine drives an electric generator mounted on the compressor shaft for producing electric power.
The use of a catalytic combustor offers the advantage that all of the fuel can be oxidized therein, resulting in ultra low NOx emissions and low CO and UHC (unburned hydrocarbon) levels. However, methods and apparatus previously described do not optimize heat exchange. Therefore, there is a need for a low-cost, reliable method to start the combustion process to bring the turbine up to operating conditions.
Thus, it is an object of the preferred embodiment to meet these and other needs.